Various devices are known in the art for treating fibers in mat form and thereafter breaking the mats into individual fibers. For example, reference is made to U.S. Pat. No. 3,440,135 to Chung which discloses a mechanism for applying a crosslinking agent to a cellulosic fiber mat, the passage of the mat while still wet and following "aging" through a fiberizer, such as a hammermill, etc. (without disclosing any specific details of such a fiberizer) to fiberize the mat, and drying the resulting loose fibers in a two stage dryer. The first dryer stage is at a temperature sufficient to flash water vapor from the fibers and the second dryer stage is at a temperature to effect curing of the crosslinking agent. A cyclone separator is then illustrated separating the fibers from the gas and for subsequent collection. Chung mentions the need for the "aging" step, of many hours duration, in order to reduce the level of nits in the resulting fiber product. As described below, nits are typically interbonded fibers which can interfere with product quality. Therefore, the Chung apparatus suffers from the drawback of requiring the inconvenient and costly storage of wet fiber mats (e.g. in roll form) for a substantial period of time in order to minimize nit formation.
Unfortunately, fiberization processes known in the art which employ currently available fiberizing or comminution machinery yield crosslinked fibers that have too many nits and knots to be acceptable for many uses. A probable reason is that such machinery has excess dead space where fibers are excessively pressed together and/or has localized regions of elevated temperature hot enough to cause premature curing of the crosslinking agent while fibers are in intimate contact with each other. Since fiberization is performed on a mat that is still wet with the uncured crosslinking agent, dead spaces and hot spots in the fiberizer would encourage the formation of interfiber bonds, which form nits, that virtually cannot be broken by downstream equipment.
Interfiber bonding in a conventional fiberizer apparatus can also lead to production of excessive amounts of "fines", which are undesirably short fibers due principally to fiber breakage. Crosslinking imparts substantial brittleness to cellulose fibers, which thereby exhibit limited compliance to mechanical stresses. Nits are especially susceptible to mechanical stresses because of their density which is much greater than the density of individual fibers. Excess fiber breakage and fines not only degrade absorbency but can substantially reduce the loft and resiliency of a product made from crosslinked fibers.
Hence, there is a need for an apparatus that will produce treated fibers, such as crosslink agent treated cellulose fibers, having a nit level lower than levels obtainable with existing equipment. There is also a need for such an apparatus that will produce such fibers from a mat comprised of cellulose fibers while not causing significant breakage of individual fibers of the mat.